1. Field of the Invention
The present invention relates to analog front-end (AFE) circuits, and more particularly, to analog front-end circuits for digital displaying apparatus and control methods thereof.
2. Description of the Prior Art
In various digital displaying apparatuses, such as the liquid crystal display (LCD) and the plasma display panel (PDP), an analog front-end (AFE) circuit is typically employed to convert the analog RGB signals into digital signals.
Please refer to FIG. 1, which shows a block diagram of a conventional analog front-end (AFE) circuit 100 of a digital display. As shown, the AFE 100 comprises a clock generator 110, a bandgap voltage reference 120, and three color processing modules 130, 140, and 150 for processing the three analog signals R, G, and B, respectively. Each color-processing module comprises a clamp circuit, a gain and offset adjusting circuit, and an analog-to-digital converter (ADC). The operations of the above components are well known in the art and further details are therefore omitted for brevity.
The performance of the analog-to-digital converters of the AFE 100 influences the image quality of the digital display. For example, in a 15-inch LCD monitor, the ADC must operate at 94.5 MHz when the displaying mode is configured to 1024*768*85 Hz (i.e., the XGA mode). In a 17-inch LCD monitor, the ADC must operate at 157.5 MHz when the displaying mode is configured to 1280*1024*85 Hz (i.e., the SXGA mode). Thus, it can be seen that the ADC must operate at higher speeds for higher resolution displaying modes.
In the conventional art, a time-interleaved ADC architecture is typically employed in the AFE circuit. FIG. 2 illustrates a simplified block diagram of an AFE circuit 200 adopting the interleaved ADC architecture according to the prior art. In the AFE circuit 200, however, the mismatch between analog-to-digital converters 220 and 230 easily results in problems such as: offset error, gain error, and phase difference. In some displaying modes or pictures, these problems become more obvious and may be detectable by human eyes. For example, an offset between the ADCs 220 and 230 may cause the presence of stripes or saw tooth artifacts in the screen image thereby negatively affecting the image quality of the digital display.